I just noticed a similar problem on an old Windows 7 machine. (Which was never upgraded due to fear of losing an old drive with Truecrypt installed on it.)
In my case, the C:\Windows directory was 272 GB! I saw other people mentioned the Installer folder but mine was a measly 18 GB, and another possibility, the winsxs folder, was just a paltry 16 GB. For me the culprit was the C:\Windows\Temp folder which weighed in at 206 GB! Fortunately, the heavyweight Temp folder had a weak chin, and I knocked it out with a single sucker punch which surprisingly took less than 30 seconds. When the bout was over all that remained were 17 small locked files that I left for the birds to eat.
Tip: I didn't delete the Temp folder; I just opened it, reverse sorted by file size, and selected everything in it, and deleted that. Some of the small files at the end were locked and I left them.
There are a lot of free windows 'file cleaners' out there that will tidy things up for you. I don't use them, so I cannot recommend one, but it should be free and open source if possible. The last thing you want is bloatware or spyware. – skub – 2012-01-15T18:17:42.020
1Get a bigger harddrive. – surfasb – 2012-01-16T23:56:08.410
Just some tips to free some space: if you don't use the hibernate function, disable it and if you have a lot of RAM, reduce the size of your pagefile.
– Gene – 2012-09-20T09:45:41.237